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<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<body>
    <script>
        function Foo() {
            Foo.a = function () {
                console.log(1);
            };
            this.a = function () {
                console.log(2);
                };
        }
        Foo.prototype.a = function () {
            console.log(4);
        };
        Function.prototype.a = function () {
            console.log(3);
        };
        Foo.a();
        // let obj = new Foo();
        // obj.a();
        // Foo.a();

        console.log(Foo.a === Function.prototype.a); // 第一次调用前：true，之后变为 false
    </script>
</body>
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